The invention relates to percussion fuses for explosive munitions shells such as mortar shells.
Conventional percussion fuse assemblies associated with mortar and other explosive munitions shells include a fuse body that interconnects the charge-carrying shell body with the shell head that is disposed forwardly of the shell body and which contains the fuse primer. The percussion cap that cooperates with the primer to detonate the charge upon shell impact, is slidably disposed within a projecting sleeve portion of the fuse body.
In order to prevent the movement of the percussion cap against the primer prior to impact of the shell, the impact member is removably secured to the overlying shell by means of at least one blocking sphere that is seated between mating grooves and bores in the periphery of the impact member and the sleeve member. In conventional designs of this type, the separable cartridge of the unfired shell extends over the outer periphery of the impact member, thereby serving to prevent the outward propulsion through the bore of the blocking sleeve. When the shell is fired within the associated weapon, the shell separates from the cartridge, whereby the blocking sphere moves outwardly through the now-open bore to bear against the inner surface of the barrel of the weapon during the further travel of the shell therethrough. The repeated rubbing of the blocking members of successive shells through the weapon establishes longitudinal grooves along the barrel, which lead to a decrease in the effective operating life of the weapon and additionally provides a leakage path for the gas pressure necessary for the firing of the weapon. The resulting diminution of gas pressure within the barrel also leads to a decrease in firing efficiency of the weapon.
Additionally, in conventional designs of this type, a helical spring or the like normally separates the front of the impact member from the rear surface of the shell head, such spring cooperating with a second inertial sphere carried in a recess at the front of the impact member to normally prevent the percussion cap from contacting the primer. Such designs have been found to be susceptible to malfunctions and premature firing, since the inertial sphere is frequently caught in the turns of the separation spring and is thereby prevented from accomplishing its desired purpose.